CloudWatch: Avoid exception while accessing results (#17283)

When accessing the `series` property of query results, if a query is
hidden, an exception is thrown. This is caused by lack of checks to
verify that the query result exists before accessing the `series`
property.

Closes #17112

public/app/plugins/datasource/cloudwatch/datasource.ts

@@ -149,6 +149,7 @@ export default class CloudWatchDatasource extends DataSourceApi<CloudWatchQuery>
       if (res.results) {
         for (const query of request.queries) {
           const queryRes = res.results[query.refId];
+          if (queryRes) {
             for (const series of queryRes.series) {
               const s = { target: series.name, datapoints: series.points } as any;
               if (queryRes.meta.unit) {
@@ -158,6 +159,7 @@ export default class CloudWatchDatasource extends DataSourceApi<CloudWatchQuery>
             }
           }
         }
+      }
 
       return { data: data };
     });